Tuesday 11 January 2011 12.47 EST
First published on Tuesday 11 January 2011 12.47 EST

Police today warned people to evacuate parts of Brisbane, Australia's third largest city, as the floodwaters which have claimed nine lives since yesterday surged towards the Queensland state capital.

The Brisbane river, which runs through the city, has already broken its banks in some areas, and residents of low-lying neighbourhoods were leaving their homes amid the worst floods in the state in decades.

About 30,000 homes face flooding, and the city authorities have warned that 9,000 will suffer "serious inundation".

The Queensland premier, Anna Bligh, said people in Brisbane and the surrounding areas were "facing their greatest threat in more than 30 years".

"We are now in a very frightening experience," she added. "Can I appeal to everybody that, at times like this, we need to all make an effort to stay calm, to be patient and to stick together."

She appealed to people to check on family and friends and offer shelter to those forced from their homes. The floodwaters are expected to peak on Thursday, at levels higher than the 1974 flood in which widespread damage was caused.

More than 70 people are missing after weeks of floods in Queensland, and police expect the death toll to rise. The dead include four children, and Bligh said many of those still unaccounted for are young children.

The whole of southern Queensland has been declared a disaster area, and military helicopters were today searching for scores of missing people. At least nine were killed yesterday when 70mm (2.8in) of rain fell in two hours, causing a wall of water to sweep through Toowoomba.

The flash flood was funnelled on to the city, upriver from Brisbane, in what police described as an "inland instant tsunami". Cars were tossed down the street, trees uprooted and businesses inundated.

"Houses were ripped from their stumps. This is unbelievable damage," the Toowoomba mayor, Peter Taylor, said.

Clem Davis, of Australia's Bureau of Meteorology, said the flash flood that struck the city, which has a population of 90,000, was fundamentally different from typical floods owing to the rising river waters.

"With general flooding, the hydrologists can actually calculate the water levels and when the peak of the flood is coming through," he told the Australian newspaper. "With a severe thunderstorm, it comes down very heavily, and therefore you can get a rapid rise in the levels."

From Toowoomba, which is 600 metres above sea level, the water flowed down the Lockyer valley and is heading towards Brisbane.

Australia's prime minister, Julia Gillard, warned that the death toll could rise. "In Queensland and around the nation, there are people who are frightened, people who are desperately waiting for news of loved ones," she said.

Reports from the town of Grantham say a wall of water up to seven metres high swept through the area. Television pictures showed houses and other buildings destroyed.

The authorities said they have grave fears for at least 30 people who had gathered in a primary school. Phone lines in the town are down.

"Our immediate focus is on the search and rescue effort in the Lockyer valley and Toowoomba," the defence minister, Stephen Smith, said.

Search and rescue services have been hampered by continuing bad weather. At least 40 people have been plucked from rooftops by emergency services. Two hundred Australian Defence Force personnel are being sent to the area to assist.

Queensland has been in the grip of floods for several weeks, with an area the size of France and Germany affected. Much of the flooding has happened in the north of the state.

"Mother nature has unleashed something shocking out of the Toowoomba region. What we have here in Queensland is a very grim and desperate situation," Bligh said.